ACID-BASE SITUATIONS.

Name: ACID-BASE SITUATIONS.
Uploaded: 2017-07-13T06:01:41+00:00
Duration: PTM52S17
Channel: Alan Payne
Description: ACID-BASE SITUATIONS.

ACID-BASE SITUATIONS

Objectives After today’s presentation you will:
List the primary causes of respiratory acidosis List the primary causes of respiratory alkalosis Given a set of electrolytes, determine the anion gap List the primary causes of a metabolic acidosis with an increased anion gap List the primary causes of a metabolic acidosis with a normal anion gap List the primary causes of a metabolic alkalosis

ACID-BASE DISTURBANCES

Respiratory Disturbances

Metabolic Disturbances

Metabolic Acidosis

General Causes of Metabolic Acidosis
Failure of kidneys to excrete metabolic acids normally found in the body. Formation of excess quantities of metabolic acids in the body. Addition of metabolic acids to the body by ingestion or infusion of acids. Loss of base from the body fluids.

Anion Gap Two ways to evaluate Na+ - Cl- - HCO3-
Normal is 6 to 12 mEq/L Na+ + K+ - Cl- - HCO3- Normal is 10 to 16

Anion Gap

Increased Anion Gap Greater than 20 = Accumulation of Fixed Acids
NORMAL CHLORIDE LEVEL MUD PILERS Methanol Uremia (Azotemic Renal Failure) Elevated BUN/Creatinine Diabetic Ketoacidosis Paraldehyde (Formaldehyde and Toluene) Isopropyl alcohol Lactic (and Formic) Acidosis Ethylene Glycol Rhabdomyolysis Salicylates

Methanol Paraldehyde Isopropyl Alcohol Ethylene Glycol Salicylates ARF Lactic Acidosis DKA Rhabdomyolysis

Normal Anion Gap INCREASED CHLORIDE LEVEL – LOSS OF BASE
Renal Tubular Acidosis No reabsorption of HCO3- Enteric Drainage Tubes Small intestine drainage – Large amounts of base in stool Diarrhea Urinary Diversion Surgical alteration of ureters Carbonic Anhydrase Inhibitors Poor reabsorption of bicarbonate

Maximum Anion Gap (mEq/L)
Low Anion Gap Look at albumin Hypoalbuminemia causes a low anion gap. Normal Albumin is 4.4 g/dL For every 0.4 g/dL decrease in albumin, the anion gap will decrease by 1 mEq/L Albumin (g/dL) Maximum Anion Gap (mEq/L) 4.4 16 4.0 15 3.6 14 3.2 13 2.8 12

Example of Extreme Compensation
On 2 L/min NC pH: 6.96 PaCO2: 6.8 mm Hg PaO2: 158 mm Hg HCO3-: 1.5 mEq/L BE: mEq/L

Metabolic Alkalosis Most common acid-base abnormality? Causes
Aggressive treatment of partially compensated respiratory acidosis? Causes Loss of Acid Vomiting NG Drainage Gain of Alkali Increased ingestion of alkaline substances Excessive licorice ingestion Hypokalemia

Advance Acid Base Interpretation

Classification vs. Interpretation
Classification: Identification of acid-base disturbance and the causative element along with any compensation that may be present. Interpretation: Use of calculations to determine if compensation is appropriate or if multiple disorders are present.

Compensation There is no such thing as overcompensation.
This usually means there is a second primary disorder at work in the opposite direction. If there is no compensation OR the compensation is less than expected: Compensation is not possible because the compensatory organ is not functioning appropriately. There has not been sufficient time for compensation (renal). Another primary disorder is present and is working in the same direction.

RESPIRATORY ALKALOSIS
PaCO2 pH HCO3- RESPIRATORY ACIDOSIS Acute ↑10 ↓ 0.08 ↑ 1 mEq/L Chronic ↓ 0.03 ↑ 4 mEq/L RESPIRATORY ALKALOSIS ↓10 ↑ 0.08 ↓ 2 mEq/L ↑ 0.03 ↓ 5 mEq/L METABOLIC ACIDOSIS ↓ 1 ↓ 0.015 ↓ 1.2 METABOLIC ALKALOSIS ↑1 ↑0.015 ↑ 0.7

Degree of Variation Allow for some degree of variation as follows:
pH: +0.03 PaCO2: + 5 mm Hg

Oakes’ Approach Primary Problem (Acidemia or Alkalemia) Primary Cause
CO2 HCO3- Compensation Initial Classification (Technical and Functional) Determine extent of compensation and the presence of other abnormalities Determine Anion Gap for metabolic acidemia Determine Oxygenation Assess Patient Check for Accuracy Final Interpretation

Factors That May Complicate Acid-Base Determination
Chronic Lung Disease Chronic Renal Disease Therapeutic interventions Mixed Acid-Base Problems

COPD Typical picture is fully compensated, respiratory acidosis.
pH: 7.38 PaCO2: 55 mm Hg HCO3-: 31 mEq/L BE: 5 mEq/L PaO2: 55 mm Hg Let’s go through the process….

7.38, 55, 31 Acidosis CO2 is elevated, so there is a respiratory cause. HCO3- is out of normal range, but is not the cause. The body is compensating. Technical Classification: Fully compensated respiratory acidosis. Functional Classification: Chronic respiratory acidosis.

7.38, 55, 31 Change in CO2: +15 torr Change in pH: -0.02
Change in HCO3-: +7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 PaCO2: 40 torr 55 HCO3-: 24 mEq/L

For every 10 torr change in PaCO2 there is a 0.03 change in pH.
7.38, 55, 31 For every 10 torr change in PaCO2 there is a 0.03 change in pH. pH D = (1.5 x .03)=0.045 =7.36 Change in CO2: +15 torr Change in pH: -0.02 Change in HCO3-: +7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 PaCO2: 40 torr 55 HCO3-: 24 mEq/L

7.38, 55, 31 For every 10 torr change in PaCO2 there is a 0.03 change in pH. pH D = (1.5 x .03)=0.045 =7.36 Change in CO2: +15 torr Change in pH: -0.02 Change in HCO3-: +7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.36 PaCO2: 40 torr 55 HCO3-: 24 mEq/L

For every 10 torr change in PaCO2 there is a 4 mEq/L change in HCO3-.
7.38, 55, 31 For every 10 torr change in PaCO2 there is a 4 mEq/L change in HCO3-. HCO3- D = (1.5 x 4)=6 24+6=30 mEq/L Change in CO2: +15 torr Change in pH: -0.02 Change in HCO3-: +7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.36 PaCO2: 40 torr 55 HCO3-: 24 mEq/L

7.38, 55, 31 For every 10 torr change in PaCO2 there is a 4 mEq/L change in HCO3-. HCO3- D = (1.5 x 4)=6 24+6=30 mEq/L Change in CO2: +15 torr Change in pH: -0.02 Change in HCO3-: +7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.36 PaCO2: 40 torr 55 HCO3-: 24 mEq/L 30

Actual HCO3- (31) doesn’t match the predicted change in HCO3-, so there must be an underlying metabolic alkalosis superimposed on the compensation. Change in CO2: +15 torr Change in pH: -0.02 Change in HCO3-: +7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.36 PaCO2: 40 torr 55 HCO3-: 24 mEq/L 30 31

For every 1 mEq/L change in HCO3- there is a 0.015 change in pH.
7.38, 55, 31 For every 1 mEq/L change in HCO3- there is a change in pH. pH D = (1 x .015) = 0.15~0.2 = 7.38 Change in CO2: +15 torr Change in pH: -0.02 Change in HCO3-: +7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.36 PaCO2: 40 torr 55 HCO3-: 24 mEq/L 30 31

7.38, 55, 31 For every 1 mEq/L change in HCO3- there is a change in pH. pH D = (1 x .015) = 0.15~0.2 = 7.38 Change in CO2: +15 torr Change in pH: -0.02 Change in HCO3-: +7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.36 7.38 PaCO2: 40 torr 55 HCO3-: 24 mEq/L 30 31

Change in HCO3-: +7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.36 7.38 PaCO2: 40 torr 55 HCO3-: 24 mEq/L 30 31

COPD So our final interpretation is a fully compensated, respiratory acidosis with a secondary metabolic alkalemia. pH: 7.38 PaCO2: 55 mm Hg HCO3-: 31 mEq/L BE: 5 mEq/L PaO2: 55 mm Hg This may be due to hypochloremia and hypokalemia associated with steroids and diuretics.

COPD – Relative Hyperventilation
If the patient below develops a hypoxemic episode (e.g. pneumonia), the resulting hypoxemia may cause the patient to hyperventilate, the PaCO2 to return to “normal”, and a metabolic alkalosis to be diagnosed. This is often seen when first starting the patient on BiPAP or mechanical ventilation pH: 7.38 PaCO2: 55 mm Hg HCO3-: 31 mEq/L BE: 5 mEq/L PaO2: 55 mm Hg pH: 7.52 PaCO2: 40 mm Hg HCO3-: 31 mEq/L BE: 5 mEq/L PaO2: 50 mm Hg Solution is to only correct the PaCO2 to 52 mm Hg

COPD with Lactic Acidosis
COPD + Reduced Cardiac Output = Cellular hypoxia and Lactic Acidosis Don’t be fooled by “normal” ABGs pH: 7.38 PaCO2: 55 mm Hg HCO3-: 31 mEq/L BE: 5 mEq/L PaO2: 55 mm Hg pH: 7.38 PaCO2: 40 mm Hg HCO3-: 24 mEq/L BE: 1 mEq/L PaO2: 44 mm Hg Loss of HCO3- due to lactic acidosis.

Chronic Renal Failure Chronic renal failure can distort ABG results.
Renal ability to manipulate HCO3-, electrolyte and fluid levels is impaired. Always evaluate with a metabolic acidosis as a possible cause.

Therapeutic Interventions
Multiple therapeutic interventions can affect acid-base balance: Diuretics Steroids Electrolytes Oxygen Sodium Bicarbonate Mechanical Ventilation

Let’s try another… Interpret this ABG: pH: 7.44 PaCO2: 18 mm Hg
[BE]: -12 mEq/L [HCO3-]: 12 mEq/L PaO2: 64 mm Hg

7.44, 18, 12 Normal, but on alkalotic side.
CO2 is reduced, so there is a respiratory cause. HCO3- is out of normal range, but is not the cause as a lowered HCO3- would not cause an alkalosis. The body is compensating. Technical Classification: Fully compensated respiratory alkalosis. Functional Classification: Chronic respiratory alkalosis.

7.44, 18, 12 Change in CO2: -22 torr Change in pH: +0.04
Change in HCO3-: -12 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 PaCO2: 40 torr 18 HCO3-: 24 mEq/L

7.44, 18, 12 For every 10 torr change in PaCO2 there is a 0.03 change in pH. pH D = (2.2 x .03)=0.066 =7.47 Change in CO2: -22 torr Change in pH: +0.04 Change in HCO3-: -12 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 PaCO2: 40 torr 18 HCO3-: 24 mEq/L

7.44, 18, 12 For every 10 torr change in PaCO2 there is a 0.03 change in pH. pH D = (2.2 x .03)=0.066 =7.47 Change in CO2: -22 torr Change in pH: +0.04 Change in HCO3-: -12 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.47 PaCO2: 40 torr 18 HCO3-: 24 mEq/L

7.44, 18, 12 For every 10 torr change in PaCO2 there is a 5 mEq/L change in HCO3-. HCO3- D = (2.2 x 5)=11 24-11=13 mEq/L Change in CO2: -22 torr Change in pH: +0.04 Change in HCO3-: -12 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.47 PaCO2: 40 torr 18 HCO3-: 24 mEq/L

7.44, 18, 12 For every 10 torr change in PaCO2 there is a 5 mEq/L change in HCO3-. HCO3- D = (2.2 x 5)=11 24-11=13 mEq/L Change in CO2: -22 torr Change in pH:+0.04 Change in HCO3-: -12 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.47 PaCO2: 40 torr 18 HCO3-: 24 mEq/L 13

Actual HCO3- (12) doesn’t match the predicted change in HCO3-, so there must be an underlying metabolic acidosis superimposed on the compensation. Change in CO2: -22 torr Change in pH: +0.04 Change in HCO3-: -12 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.47 PaCO2: 40 torr 18 HCO3-: 24 mEq/L 13 12

7.44, 18, 12 For every 1 mEq/L change in HCO3- there is a change in pH. pH D = (1 x .015) = 0.15~0.2 = 7.45 Change in CO2: -22 torr Change in pH: +0.04 Change in HCO3-: -12 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.47 PaCO2: 40 torr 18 HCO3-: 24 mEq/L 13 12

7.44, 18, 12 For every 1 mEq/L change in HCO3- there is a change in pH. pH D = (1 x .015) = 0.15~0.2 = 7.45 Change in CO2: -22 torr Change in pH: +0.04 Change in HCO3-: -12 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.47 7.45 PaCO2: 40 torr 18 HCO3-: 24 mEq/L 13 12

The predicted pH of 7.45 is within the degree of variation of for pH. Change in CO2: -22 torr Change in pH: +0.04 Change in HCO3-: -12 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.47 7.45 PaCO2: 40 torr 18 HCO3-: 24 mEq/L 13 12

Interpretation Fully compensated respiratory alkalosis with simultaneous metabolic acidosis.

Mixed Acid-Base Disturbances
Sometimes a simple compensatory mechanism isn’t the reason for the normalized acid-base status. If two opposing problems co-exist (ARF causing metabolic acidosis and pain causing respiratory alkalosis), you may have what looks like one compensating for the other.

Interpret this ABG: pH: 7.38 PaCO2: 20 mm Hg [HCO3-]: 17 mEq/L
PaO2: 89 mm Hg

7.38, 20, 17 Normal, but on acidotic side.
CO2 is reduced, which would not cause an alkalosis. HCO3- is reduced and would cause an alkalosis. The body is compensating. Technical Classification: Fully compensated metabolic acidosis. Functional Classification: Metabolic acidosis.

7.38, 20, 17 For every 1 mEq/L change in HCO3- there is a change in pH. pH D = (7 x .015)=0.105 =7.30 Change in CO2: -20 torr Change in pH: -0.02 Change in HCO3-: -7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 PaCO2: 40 torr HCO3-: 24 mEq/L 17

7.38, 20, 17 For every 1 mEq/L change in HCO3- there is a change in pH. pH D = (7 x .015)=0.105 =7.30 Change in CO2: -20 torr Change in pH: -0.02 Change in HCO3-: -7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.30 PaCO2: 40 torr HCO3-: 24 mEq/L 17

7.38, 20, 17 Change in CO2: -20 torr Change in pH: -0.02
The calculated change in pH (7.30) differs from the actual measured pH, so there must be some additional acid-base disturbance. Change in CO2: -20 torr Change in pH: -0.02 Change in HCO3-: -7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.30 PaCO2: 40 torr HCO3-: 24 mEq/L 17

For every 1 mEq/L change in HCO3- there is a 1.2 change in PaCO2.
7.38, 20, 17 For every 1 mEq/L change in HCO3- there is a 1.2 change in PaCO2. PaCO2 D = (7 x 1.2)=8.4 40-8.4=31.6~32 Change in CO2: -20 torr Change in pH: -0.02 Change in HCO3-: -7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.30 PaCO2: 40 torr HCO3-: 24 mEq/L 17

The calculated change in PaCO2 (32) differs from the actual measured PaCO2, so there must be a respiratory disturbance present. Change in CO2: -20 torr Change in pH: -0.02 Change in HCO3-: -7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.30 PaCO2: 40 torr 32 HCO3-: 24 mEq/L 17

The difference between the calculated change in PaCO2 (32) and the actual PaCO2 (20), indicates that there must be a respiratory disturbance present. Change in CO2: -20 torr Change in pH: -0.02 Change in HCO3-: -7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.30 PaCO2: 40 torr 31.6 20 HCO3-: 24 mEq/L 17

7.38, 20, 17 For every 10 torr change in PaCO2 there is a 0.08 change in pH. pH D = (1.2 x .08)=0.096 =7.396 Change in CO2: -20 torr Change in pH: -0.02 Change in HCO3-: -7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.30 PaCO2: 40 torr 31.6 20 HCO3-: 24 mEq/L 17

The predicted pH is within the level of variability of 0.03 units.
7.38, 20, 17 The predicted pH is within the level of variability of 0.03 units. Change in CO2: -20 torr Change in pH: -0.02 Change in HCO3-: -7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.30 7.40 PaCO2: 40 torr 31.6 20 HCO3-: 24 mEq/L 17

Interpretation Mixed metabolic acidosis and simultaneous respiratory alkalosis.

Can you have a triple disorder?

Anion & Bicarbonate Gaps
Anion Gap: Na+ - Cl- - HCO3- Normal value is 6 to 12 Above 20 considered High Bicarbonate Gap: HCO3- + (AG-12) Normal is 20 to 28 – AG Metabolic Acidosis Less than 20 – AG Metabolic Acidosis + Non-AG Metabolic Acidosis Greater than 28 – AG Metabolic Acidosis + Metabolic Alkalosis

7.52, 30, 21 Alkalemia. CO2 is reduced, which would cause an alkalosis. Primary respiratory alkalosis. HCO3- is reduced and would not cause an alkalosis. The body is compensating (HCO3- decreasing) Technical Classification: Partially compensated respiratory alkalosis. Functional Classification: Chronic respiratory alkalosis.

7.52, 30, 21 For every 10 torr change in PaCO2 there is a 0.03 change in pH. pH D = (1 x .03)=0.03 =7.43 Change in CO2: -10 torr Change in pH: +0.12 Change in HCO3-: -3 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 PaCO2: 40 torr 30 HCO3-: 24 mEq/L

7.52, 30, 21 For every 10 torr change in PaCO2 there is a 0.03 change in pH. pH D = (1 x .03)=0.03 =7.43 Change in CO2: -10 torr Change in pH: +0.12 Change in HCO3-: -3 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.43 PaCO2: 40 torr 30 HCO3-: 24 mEq/L

The calculated change in pH (7.43) differs from the actual measured pH, so there must be some additional acid-base disturbance. Change in CO2: -10 torr Change in pH: +0.12 Change in HCO3-: -3 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.43 PaCO2: 40 torr 30 HCO3-: 24 mEq/L

7.52, 30, 21 For every 10 torr change in PaCO2 there is a 5 mEq/L change in HCO3-. HCO3- D = (1 x 5)=5 24-5=19 mEq/L Change in CO2: -10 torr Change in pH: +0.12 Change in HCO3-: -3 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.43 PaCO2: 40 torr 30 HCO3-: 24 mEq/L

7.52, 30, 21 For every 10 torr change in PaCO2 there is a 5 mEq/L change in HCO3-. HCO3- D = (1 x 5)=5 24-5=19 mEq/L Change in CO2: -10 torr Change in pH: +0.12 Change in HCO3-: -3 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.43 PaCO2: 40 torr 30 HCO3-: 24 mEq/L 19

The calculated change in HCO3-differs from the actual measured HCO3-, so there must be some additional acid-base disturbance. Change in CO2: -10 torr Change in pH: +0.12 Change in HCO3-: -3 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.43 PaCO2: 40 torr 30 HCO3-: 24 mEq/L 19 21

7.52, 30, 21 For every 1 mEq/L change in HCO3- there is a change in pH. pH D = (2 x .015)=0.03 =7.46 Change in CO2: -10 torr Change in pH: +0.12 Change in HCO3-: -3 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.43 PaCO2: 40 torr 30 HCO3-: 24 mEq/L 19 21

7.52, 30, 21 For every 1 mEq/L change in HCO3- there is a change in pH. pH D = (2 x .015)=0.03 =7.46 Change in CO2: -10 torr Change in pH: +0.12 Change in HCO3-: -3 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.43 7.46 PaCO2: 40 torr 30 HCO3-: 24 mEq/L 19 21

Note that the pH still is not fully explained by the change in bicarbonate due to compensation. Some additional metabolic alkalosis must be present. Change in CO2: -10 torr Change in pH: +0.12 Change in HCO3-: -3 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 7.43 7.46 PaCO2: 40 torr 30 HCO3-: 24 mEq/L 19 21

Look to Anion & Bicarbonate Gaps
Na+: 142 mEq/L Cl-: 98 mEq/L AG: Na+ - Cl- - HCO3- = = 23 This means we have an Anion Gap Metabolic Acidosis BG: HCO3- + (AG-12) = 21 + (23-12) = = 32 AG Metabolic Acidosis + Metabolic Alkalosis

Interpretation Primary respiratory alkalosis and metabolic acidosis and metabolic alkalosis. Huh? An example would be a patient with pneumonia who is hyperventilating secondary to hypoxemia, who also has azotemic renal failure and has hypokalemia secondary to aggressive diuretic therapy.

Change in HCO3-: -3 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 PaCO2: 40 torr 30 HCO3-: 24 mEq/L

Can you have a quadruple disorder?

Acid-Base Map Fig 14-1

pH: 7.35 PaCO2: 60 mm Hg

Fun reading… Last part of Chapter 14 in Malley.

Change in HCO3-: +7 mEq/L BASELINE Disorder #1 Disorder #2 pH: 7.40 PaCO2: 40 torr 55 HCO3-: 24 mEq/L

ACID-BASE SITUATIONS.

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